f2fs: Fix data corruption issue with FBE

Fix FBE regression with commit -
<207991d5>("f2fs: add bio cache for IPU"). The above commit
is not setting the DUN for bio, due to which the bio's could
get corrupted when FBE is enabled.

Change-Id: Iebf0637dd524053d1a67ef594a9494a36d2a31b3
Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>